The invasion from Akavir was only 10-15 years before the start of the game according to this video. http://www.gameinformer.com/b/features/archive/2012/05/21/creating-the-story-for-the-elder-scrolls-online.aspx
This is also not that long after the Remnan dynasty and the Akaviri Potentate. So Akaviri could still be un-assimilated.
Knowing that there were multiple invasions from Akivir over the years, we could even see another invasion later on as a DLC or special event.
What do you guys think?